How does one make a car lightweight (for high acceleration) and yet rigid enough to maintain precise control? Easy as it seems, it is not so, as the two qualities are in direct conflict. That is where engineering design plays a role.
A space frame is a model of a structure built from strong links connected by freely rotating joints so that the structure is perfectly rigid. Like in a bridge built from triangles, which is the fundamental space frame.
This is also the case where a separate chassis is chosen to build a vehicle upon. "It is like a skeleton on which discrete components are fixed," explains Prof Anindya Deb, Centre for Product Design and Manufacture, IISc.
However most car makers prefer what is called a unibody model which is lighter and easier to build. It is the trucks which need to navigate rough terrain which have resorted to chassis. What Anindya Deb's team at CPDM did was to build the first space frame car using aluminium extrusions.
The advantages of a chassis are in the strength and relative simplicity of its architecture, but safety requirements, fuel economy have seen a demand for design change. World-over there is a shift to unibody that comes with a good crushability factor and strength as well as easy production.
However using Aluminium, Deb says that the spaceframe is also good for a light weight car, not just trucks. "It has much potential as it uses less material and compensates for the high cost."
As good as steel
Aluminium is energy efficient and from a lifecyle point of view is more environment friendly than steel. Being recyclable and not corrosive, it has advantages.
As to the strength to weight ratio too, it is as good as steel, he says. It is light and has less strength while steel is heavy and high strength.
However, aluminium welding is still a tricky problem as also welding together different materials.
The department is now building a spaceframe for a van.
Anindya has experience in automotive world, having worked with Telco in Jamshedpur and Ford in Michigan. The centre has come out with tools for various companies like GM, Mahindra and Mahindra, Tata Motors, etc. "In fact, we helped reduce the weight of Scorpio."
The design time for a car used to be ten years but has now come to 24 months due to CAE (computer aided engineering), he says.
Design and emotions
The centre also has ‘designs with emotions’! Here various aspects of the hard and soft categorization of cars is studied upon where sharp lines represent aggression and hardness. "We can also categorise its features as soft and aggressive," says Anindya. The next step is the engineering design that looks at shape, size, safety, etc.
"Software is available but the model varies for each product. We need the mathematical models to check how a vehicle would be affected in an accident, or how the bumps would be handled, etc. These simulations are done at our centre using finite element model. It has helped to cut down on prototypes. However, with small components, that are complex we still need product testing. At the macro level, flaws can be averaged out," the professor, who is on the board of two international journals on safety, says.
We pay a lot of attention to the safety aspect, he adds.
Glass metals
Function, shape, process and material are important factors when manufacturing. Designs come at various levels. Materialistic designs are as important in the world of products manufacture.
G Ravichandran, Caltech, has taken up the challenge of making and studying bulk metallic glass, or glassy metals! He was in India during a recent expo on design in manufacture and engineering, The Engineering Design.in 2007 saw many national and international take part in discussions around the latest in the field as also the problems faced.
In any material important properties are elasticity, yield, hardness, fracture toughness and fatigue. In engineering materials and making composites, ceramic, polymers, elastomers and glasses have been looked at. But each has its limitations.
In metals the elastic limit of 0.2 is its limiting aspect but costs make up. Polymers have high yield but strength is low.
That is where glass alloys come in, explains Ravichandran. With their high elastic limit, polycrystalline materials like Vitreloy 1 or metallic glass composites are ideal materials.
Glass alloys when cooled slowly are amorphous, meaning they have no melting point. (If cooled fast, they become crystalline.) Being rubbery they can be processed easily. They have superior mechanical properties like high yield strain, high hardness, etc.
Superplastic
However they do not deform homogenously. If this can be prevented they can have superplastic formability. This can be achieved at high temperatures, it was discovered.
"With superplasticity, they lend themselves to surgical tools, jewellery, etc with fine features. Also a high production rate with the fine features makes them excellent for MEMs applications," says the scientist. With ductility being size dependent, at low thickness they can be bent highly.
Aerospace applications (due to high specific strength), in mobiles, computers, watches (due to light weight plus high strength) and in golf clubs (due to high elastic strain) are some of the uses of glass metals.

CPDM courses
The Centre for Product Design and Manufacturing (CPDM) was established to pursue excellence in teaching, research and industry interaction in the area of Design. The two-year M.Des programme is the flagship program of the Centre. The Centre pursues an active research programme in design spanning the broad areas of Design Theory and Methodology, Human Factors in Design, PLM and, Vehicle Design, Simulation and Testing.
 The core competency of CPDM lies in the successful amalgamation of research in design (M.Sc.(Engg.) and Ph.D.) and design in practice (M.Des.). CPDM firmly believes that product designers and design researchers are complementary to each other. While designers create products to improve the society, design researchers develop effective design methods and techniques for better design.
Visit www.cpdm.iisc.ernet.in